Broken back circuit breaker contact



July 11, 1950 A. s. CASWELL BROKEN BACK CIRCUIT BREAKER CONTACT 4 Sheets-Sheet 1 Filed June 17, 1944 INVEA" TOR.

ATTORNEY July 11, 1950 A. s. CASWELL BROKEN BACK CIRCUIT BREAKER CONTACT 4 Sheets-Sheet 2 Filed June 17, 1944 INI 'EN TOR.

ARTH UR S. CASWELL ATTORNEY July 11, 1950 A. s. CASWELL 2,514,839

BROKEN BACK cmcurr BREAKER CONTACT Filed June 17, 1944 4 Sheets-Sheet 3 24 33 an I88 2% 5 INVENTOR. F 5 3 V ARTHUR s. CASWELL ZJW ATTORN EIY July 11, 1950 A. s. CASWELL BROKEN BACK CIRCUIT BREAKER CUNTACT 4 Sheets-Sheet 4 Filed June 1'7, 1944 L m a Va s m A 8 F ATTORNEY Patented July 11, 1950 BROKEN BACK CIRCUIT BREAKER CONTACT Arthur S. Caswell, Philadelphia, Pa., asaignor to I. T. E. Circuit Breaker Company, Philadelphia, Pa., a corporation of Pennsylvania Application June 17, 1944, Serial No. 540,803

4 Claims.

My present invention relates to circuit interrupters and more specifically to a simple and rugged contact structure therefor.

My invention contemplates that the main and arcing contacts and their supporting members he made of solid pieces of metal, devoid of small springs, pins, washers and other fragile parts usually thought to be necessary on moving contact structures for circuit interrupters.

Such small light weight parts made necessary by prior contact structures are usually present in the arcing area wher they are vulnerable to the arc flash which may cause them to fuse, melt or disintegrate. This condition has always been undesirable since it upsets breaker adjustment and reduces the efllciency of the equipment.

My invention has for its object the provision of a simple rugged construction for the moving contact in the arcing area, which construction nevertheless is light in weight; thus reducing the inertia of the contact arm and thereby speeding the breaking action of the contacts.

A primary object of my invention is the formation of a movable contact carrying arm in such manner that the contact arm itself forms a toggle or broken back" arrangement which will permit a wiping action of the contacts to occur, will multiply the closing force for increased contact pressure, and, at the same time, will increase the opening speed.

A further object of my invention is the provision of a novel blow-on" contact arrangement where the magnetic forces induced by the current flow are used to reinforce the contact pressure.

Many other objects of my invention will become apparent in the following description and drawings in which:

Figure 1 is a side view partly in cross-section of my novel circuit breaker contact construction with the arcing contacts closed and before the main contacts have engaged, taken on line |-l of Figure 3 looking in the direction of the arrows.

Figure 2 is a side view corresponding to that of Figure 1 showing in solid lines the contact structure in closed position, and in dotted lines the contact structure in fully opened position.

Figure 3 is a front view partly broken away of the movable contact structure.

Figures 4, 5, 6 and '7 are schematic views showing the operation of the circuit breaker of Figures 1 to 3.

Referring now to Figures 1, 2 and 3, the circuit ireaker It comprises an upper connecting memer H and a lower connecting member II. The pper connecting member has secured thereto in 2 any suitable manner an arcing contact I3 and a main contact it. These form the stationary contacts.

The movable contact carrying arm' l5 comprises a first supporting movable arm I1 and a second movable arm I 6. Movable arm I6 is pivotally mounted on Pivotal support or bolt l9. Movable arm l6 carries a pivot it on which the supporting arm I! is itself pivotally mounted.

The additional arm ll carries at the upper end thereof the movable arcing contact 20 and arcing horn 2| and the movable main contact 22.

It will be seen from a comparison of the solid line positions of Figures 1 and 2 that arms i1 and it are in toggle relation, with the link ll of the toggle being stationarily pivoted at IS, the knee pin of the toggle being formed by the pin It and the opposite pivot of the toggle being formed during the closing operation, first, by the ageing contact 20 and then by the main contact 2 The pigtail-less construction herein shown, wherein the current is carried between rotatably related parts through ball bearings rather than through pigtails, is based on the disclosure of application Serial No. 480,619, of Otto Jensen, filed March 26, 1943, now abandoned.

The lower supporting arm I8, as seen in Figure 3, is a compound arm formed by the members lta and lib which are rotatable about the bolt I9. Likewise, the front end of the lower connector i2 comprises a pair of plates |2a and I 2b.

A ball bearing carrier 25 is mounted on each side between plates lib and Ito and the filler rings 28, which filler rings bear against plates [2a and Rh.

A bolt I9 passes through corresponding openings in all of the members I211, 25, 26, "5b, Ita and l2b.

An additional filler ring 26a is provided between plates lia and ilib in order properly to space them and to provide a surface against which the nut 29 may be tightened.

Spring washers 28 on the outside of the plates Ho and i212 are held in position by tightening the nut 29 on the bolt l9 and locking it in place by the lock nut 29a. The spring washers 28 ensure adequate pressure so that the ball bearings carried by the ball bearing rings 25 may carry current effectively from the supporting arm It to the lower connecting member l2.

Similarly, the additional arm I1 is pivotally mounted on the supporting arm is in such a manner that a rotatable current carrying engagement exists.

I1 rotates with respect to the supporting arm I is composed of two special cap screws, 45 and 28. The cap screw 38 passes through the supporting arm lBb, ball carrying ring 30, additional arm Ila and spring washer 2i. It is held in place and tightened to give proper contact pressure by the nut 23.

The cap screw 39 passes through corresponding parts on the right hand side of the contact arm, but is somewhat different from cap screw II in that its head is drilled at llb in order to receive the separating adjusting screw "a.

The separating adjusting screw "a, held in adjustment by spring lock 34, being threaded into the cap screw 39 and having'its head lBc bearing on the head 33 of the cap screw it maintains the distance between the supporting arms i511 and I61) and the additional arms I la and 1 1b. This adjustment will keep these parts parallel and thereby overcome distortion due to high currents which will tend to' draw the arms together and cause unequal contact pressure on the Joints.

A ball bearing carrying ring 30 is mounted between each pair of plates i1a'-I5b and i1b-l6a to form a current carrying conductive path therebetween in the manner described in application Serial No. 480,619 above mentioned.

Spring washers 2|, 2| captured between the outermost plates Fla and "b and the respective bolt head and nut head, serve to ensure proper contact pressure.

The main movable contact member 22, which, as can be seen from Figure 2 is a compound member, is secured to the rear flanges l1c of the additional arm 11 by the bolt 35 and'is anchored at the front flanges l1a. by the bolts 26.

Vertical extensions 31, 31 of the contact members 22 support the arcing horn 2| and the arcing contact 20.

An operating means for operating the arm l1 comprising a link 40 from the operating mechanism is pivoted on a pin 4i carried between the plates Ma. and ill) of the additional supporting arm i1.

The upper ends of the plates I Ga and itb are each provided with the elongated slot 42 which is substantially longerthan the diameter of the pin 4|.

A spring member 45 is arranged to bias th lower end of the additional arm l1 so that the same will tend to rotate in counterclockwise direction around the pivot l8. One end of the spring 45 engages the end of lug 46 which is pivoted at 41 on the control arm 48 which, in turn, is pivoted at 49 on the lower connector l2.

Lug 46 is provided with a U-shaped or hair-pin extension 50 which centers the spring 45. A guide pin i on the lower conductor l2 passes through the central slot of the hair pin extension 50. The other 'end of the spring .45 bears against the guide pin 5i so that the spring is compressed between members 45 and 5!.

The control arm 48 and the guide pin 5| limit the expansion of the compression spring 45 after the moving contact arm separates from the stationary contacts.

Essentially, it-will be seen that the arms l1 and I6 form a toggle, the knee pin of which is is rotatably supported on the stationary pivot II.

The action of the compression spring 45 ensures that the arms i1 and it of the tog le will remain in broken" condition. The rotation of the additional arm i1 around the supporting arm i8 is limited, of course, by slot 42. Nevertheless, it will be seen that as the link 40 forces the toggle toward closed position, the compression spring 45 maintains the broken" condition of the arm until the contacts are fully engaged.

During the closing operation (while the contact structure moves from the position shown by the dotted lines of Figure 2 to the position shown by the solid lines of Figure 2), the structure 15 passes through the intermediate stage of Figure 1. That is, as the link 40 is forced toward the left with respect to Figure 1, it pushes the pin 4! to the left and consequently pushes the entire additional arm IT to the left. The pin 4i also engages the left hand end of the slots 42 of the support arm iii to rotate the supporting arm I! in a counterclockwise direction toward the left. The spring 45 pushes the flange no of arm i1 up against the plates of the supporting arm i5, maintaining the "broken condition of the toggle i1i8-I6. This arrangement of the members continues as the link 40 pushes the contact arm I5 toward the closed position.

It will be noted that the elements above described maintain the additional arm H in such relation to the supporting arm it that the movable arcing contact 20 will strike the stationary arcing contact i3 first (as seen in Figure 1).

Further movement of the link 40 toward the left will continuously urge the pin 4i toward the left. Since now the end 20 (the arcing contact) of the arm l1 has reached its limit of movement toward the left, then the lower end 55 of the arm i1 is the only portion thereof which is free to move any further toward the left. Continued.

movement of the link 40 toward the left will now, therefore, further compress the spring 45 and will straighten out the toggle i1|8-i6 formed by the supporting arm and the additional arm.

As the toggle is thus straightened out, the main contact member 22 of the additional supporting arm l1 engages the main stationary contact member i4 while the arcing contacts 26 and i3 separate. This condition is shown by the solid lines of Figure 2.

The foregoing operation may also be readily understood from an examination of the schematic showings of Figures 4, 5, 6 and 7, where the operating mechanism 60 is operable to drive the link 40 to the left to cause engagement of the contacts, and where the mechanism may be tripped in any suitable manner to effect separa- Figure 7 shows the open circuit position corresponding to the dotted line position of Figure 2. On movement of the connecting link 40 to the left, the additional arm I1 is driven to the left, as above described, while the spring 45 maintains the broken condition of the toggle i1--i8-i6. The pin 4i at the end of the link 40 also drives the supporting arm i6 toward the left through the slot 42.

Since the toggle l1'l8i6 is in broken condition with the upward end of the arm i1 inclined toward the left, the arcing contacts 20 and i3 will engage first as seen in Figure 6. Once the upper end 20 (the arcing contact) of arm i1 can no longer move to the left, then the lower end 55 of this arm is the only one which may move to the pivot I8; and the lower end of the arm I the left, and continued movement of the link 45 to the left, as shown in Figure 5, will now cause engagement of the main contacts I and 22. Further continued movement of the link ll to the left will, as shown in Figure 4, increase the contact pressure of the main contacts I and 22 and separate the arcing contacts II and It.

This "broken back? arrangement of the movable contact arm provides for proper sequential closing of the circuit breaker contacts; that is, the arcing contacts close first and the main contacts close last.

Similarly, during the opening operation, the condition is reversed and the main contacts separate first and the arcing contacts separate last.

The particular overload responsive mechanism by which the contacts are disengaged has not been disclosed, as any well known mechanism may be employed.

As is well known in the art, when an abnormal circuit condition of any nature, such as a short circuit, occurs, trip mechanism functions to operate the link 40 to the right to effect tripping of the circuit breaker.

Thus, examining Figures 4, 5, 6 and 7 in reverse order from the examination previously followed, Figure 4 shows the closed position.

On tripping of the circuit breaker, which tends to pull the link 40 to the right, the lower end 55 of the arm I! will first move to the right around the pivot it until the pin 4| strikes the left hand end of the slot 42 in the supporting arm It. Before the pin 4i strikes the left hand end of the slot 42, the arcing contacts have engaged while the main contacts still remain in engagement (Figure Then, as the pin ll strikes the left hand end of slot 42 and the toggle |||l-ll can break no further, the main contacts H2Lseparate while the arcing contacts "-20 remain engaged (Fig.6).

Finally, on further movement of the link 40 toward the right, the contacts reach the open circuit position of Figure '7.

This "broken back construction for the movable contact arm of the circuit breaker gives the necessary resilience for closing and proper contact pressure.

The simple and rugged construction in the contact area is an important feature of this novel contact bridge or contact arm design. The main and arcing contacts and the supporting members are made of solid pieces of metal devoid of small springs, pins, washers and other fragile parts which have thus far been necessary to secure proper adjustment and contact pressure. Such light weight parts, usually present in the arcing area in prior circuit breaker designs are vulnerable to the arc flash which may cause them to fuse, melt or distintegrate. This has always been undesirable, since it upsets the circuit breaker adjustment and reduces the efllciency of the equipment. The simple rugged construction in the arcing area herein shown eliminates this objectionable feature.

Furthermore, a minimum of weight, as herein shown at the end of the bridge arm opposite the pivot point, reduces the inertia of the bridge arm and thereby speeds the breaking action of the contacts.

Natural electromagnetic phenomena are utilized in this contact structure so that the magnetic forces set up by high currents would tend to force the contact points together instead of separating them. This occurs because the length of the contact arm between the main pivot point II and the pin I (Figure 1) is much longer than the distance from the pin 4| to the arc tip 20: this causes the magnetic forces to be greater below the pin and thereby force the are tips together.

This may be explained as follows: When a short circuit occurs, the current flowing from stud 12 through the arm IE to arm I! and back over stud ll sets up magnetic forces on arm I to drive it clockwise about its pivot It. This mag,- netic force acting on arm i8 is transferred through pin it to the arm 11 tending to rotate it counterclockwise about the pin 4| (which at this instant is still stationary) in a counterclockwise direction and therefore increasing the contact engagement of. contacts is and 22.

The same magnetic force acting on arm I! below pin 4| tends to rotate arm I! counterclockwise about li, thus adding to, the first force. That portion of this magnetic force acting between pin ti and contact it tends to rotate arm I 1 in a clockwise direction about pin H. The length of the arm from II to contact it being shorter than the arm from the bottom of I! to pin 4|, the resultant force on arm I! is still a counterclockwise rotation about I 8 additive to the force applied thereto from arm it.

As the pin ll moves away, arm I! applies a force effecting a rotation thereof on contact 22 as a fulcrum untilthe arcing contacts 13 and 20 engagethe condition obtained in Figure l. The magnetic forces between 19 and 4| acting on arm l8 and through pin l8 continue to act on arm I! applying a counterclockwise force therein about pin 4|. This force, plus direct force on arm 11, is greater than the clockwise force on arm I! from pin I to contact 20, thus insuring good contact engagement of the arcing contacts until they disengage.

As will be obvious from a comparison of Figures 2 and 1, a further desirable feature obtained with this type of construction is the wiping effect of the contact surfaces. with the loose motion in the bridge, due to the broken back construction, when contact surfaces meet, they slide across each other for a short distance until the bridge is finally latched. This wiping action reduces the amount of foreign particles that come between the contact surfaces and thereby reduces the resistance of the contacts.

The loose, springy action of this design produces the necessary resilience for properly closing and latching the contacts. This bit of elasticity, or free motion, allows sufficient pressure to be exerted to make good contact and at the same time permits the closing latch to be actuated without an abnormal force having to be applied.

My invention thus increases the speed with which the contact a-rm may act, simplifies the construction, and thereby makes possible lower manufacturing costs, quicker and easier assembly and sturdier parts which are less likely to get out of adjustment. All of these elements are obtained while, at the same time, retaining or improving the blow-on features, the wiping action, the speed of contact separation and the butt type contacts.

In the foregoing, I have described my invention only in connection with a specific preferred embodiment thereof. Since many variations and modifications of the construction herein shown within the spirit of my invention should now be obvious to those skilled in the art, I prefer to be bound not by the specific disclosures herein but only by the appended claims.

I claim:

1. In a circuit breaker, a first movable arm, a

tact and arcing contact respectively,- a second.

movable arm, a pivotal support, said second movable arm being pivotally supported at one end thereof on said pivotal support, a lower connecting member connected to said second movable arm, a pivot on said second movable arm, said first movable arm being pivotally supported on said last-mentioned pivot, a pin secured to said first arm intermediate said pivot and said contacts on said first movable arm, an operating mechanism secured to said pin, the distance from said pivotal support to said pin being greater than the distance from said pin to said arcing contacts, said second arm having an elongated slot at its end opposite from said pivotal support, said pin extending in said slot, a spring member engaging said first movable arm at the end opposite from the end at which said contacts are secured. said spring tending to rotate said first arm about said pivot on said second arm toward engagement of said contacts, said operating mechanism operating said first arm through said pin toward contact engaging position and said second arm about said pivotal support through said pin in engagement with one end of said slot until said arcing contacts engage, further movement of said operating mechanism moving said second arm alone until the arcing,

contacts separate, the magnetic forces set up by currents flowing in the loop circuit comprising the two connecting members and the two movable arms acting on said second arm being transferred through said pivot to said first arm tending to rotate it counterclockwise about said pin to increase the contact pressure of said main contacts, said magnetic forces acting on said first arm be- 'low said pin tending to rotate said first arm counterclockwise and acting on said arm above said pin tending to rotate said first arm clockwise, the length of said first arm from said pin to said main contacts being shorter than from the opposite end of said first arm to said pivot so that the resultant of said last two magnetic forces is additive to said first-mentioned magnetic force during movement of said operating mechanism in response to said fault current, said first arm applying a force effecting rotation about said main contacts as a fulcrum until said arcing contacts engage, the magnetic forces between said pivotal support and said pin acting on said second arm and through said pivot acting on said first arm producing a force about said pin to increase contact pressure and said force acting directly on said first arm below said pin being greater than the force on said first arm from said pin to said arcing contact to ensure good arcing contact engagement.

2. In a circuit breaker, a first movable arm, a

rigidly mounted main contact and arcing contact secured to one end of said arm, an upper connecting member, a rigidly mounted main contact and arcing contact on said connecting member engageable by said first-mentioned main contact and arcing contact respectively, a second movable arm, a pivotal support, said second movable arm being pivotally supported at one end thereof on said pivotal support, a lower connecting member connected to said second movable arm, a pivot on said second movable arm, said first movable arm being pivotally supported on said lastsmentioned pivot, a pin secured to said first arm intermediate sai d pivot and said contacts on said first movable arm, an operating mechanism secured to said pin, the distance from said pivotal support to said pin being greater than the distance from said pin to said arcing contacts, said second arm having'an elongated slot at its end opposite from said pivotal support, said pin extending in said slot, a spring member engaging said first movable arm at the end opposite from the end at which said contacts are secured, said spring tending to rotate said first arm about said pivot on said second arm toward contact engagement, said operating mechanism operating said first arm through said pin toward contact engaging position and said second arm about said pivotal support through said pin in engagement with one edge of said slot until said arcing contacts engage, the length of said first arm from said pin to said main contacts being shorter than from the opposite end of said first arm to said pivot, said first arm applying a force effecting rotation of said main contacts as a fulcrum until said arcing contacts engage, the magnetic forces, due to currentfiowing in said loop, between said pivotal support and said pin acting on said second arm and through said pivot acting on said first arm producing a force about said pin, and said force acting directly on said first arm below said pin being greater than the force on said first arm from said pin to said arcing contact to ensure good arcing contact engagement.

3. In a circuit breaker, a first movable arm, a rigidly mounted main contact and arcing contact secured to one end of said arm, an upper connecting member, a rigidly mounted main contact and arcing contact on said connecting member engageable by said first-mentioned main contact and arcing contact respectively, a second movable arm, a pivotal support, said second movable arm being pivotally supported at one end thereof on said pivotal support, a lower connecting member connected to said second movable arm, a pivot on said second movable arm, said first movable arm being pivotally supported on said last-mentioned pivot, a pin secured to said first arm intermediate said pivot and said contacts on said first movable arm, an operating mechanism secured to said pin, the distance from said pivotal support to said pin being greater than the distance from said pin to said arcing contact, said second arm having an elongated slot at its end opposite from said pivotal support, said pin extending in said slot, a member. engaging said first movable arm at the end opposite from the end at which said contacts are secured, said member tending to rotate said first arm about said pivot on said second arm toward contact engagement, the length of said first arm from said pin to said main contact being less than the length from said pin to the opposite end of said first arm. v 4. In a circuit breaker, a first movable arm, a rigidly mounted main contact and arcing contact secured to one end of said arm, an upper connecting member, a rigidly mounted main contact and arcing contact on said connecting member engageable by said first-mentioned main contact and-arcing contact respectively, a second movable arm, a pivotal support, said second movable arm being pivotaliy supported at one end thereof on said pivotal support, a lower connecting member connected to said second movable arm, a pivot on said second movable arm, said first movable arm being pivotally supported on said last-mentioned pivot, a pin secured to said first arm intermediate said pivot and said contacts on said first movable arm, an operating mechanism secured to said pin, the distance from said pivotal support to said pin being greater than the distance from said pin to said arcing contacts, said second arm having an elongated slot at its end opposite from said pivotal support, said pin extending in said slot, a member engaging said first movable arm at the end opposite from the end at which said contacts are secured, said member tending to rotate said first arm about said pivot on said second arm toward contact engagement, the length of said first arm from said pin to said main contact being less than the length from said pin to the opposite end of said first arm, said pin acting as a fixed pivot 5 during tripping in response to fault current.

ARTHUR S. @ASWEm.

REFERENCES CITED The following references are of record in the 10 file of this patent:

UNITED STATES PATENTS 

